[Criteria for social isolation based on associations with health indicators among older people. A 10-year follow-up of the Aichi Gerontological Evaluation Study].

OBJECTIVES: No clear evidence for a cut-off point for social isolation has been established so far. The purpose of this study was to evaluate the criteria for social isolation based on associations with objective health outcomes in a 10-year follow-up study.
METHODS: We performed a prospective study of functionally independent residents aged 65 years or older who lived in six municipalities as part of the Aichi Gerontological Evaluation Study (response rate: 50.4%) that began in 2003. Data on the onset of functional disability, dementia, and death were obtained from municipal databases of the public long-term care insurance system. A total of 12,085 participants were followed up for up to 10 years. We used frequencies of face-to-face and non-face-to-face contact with non-resident children, relatives and friends, or neighbors as indicators of social isolation. The overall frequency of contact with others was categorized from "less than once a month" to "frequently, every day."
RESULTS: Cox's proportional hazard model revealed that, after controlling for sex, age, education level, marital status, equivalent household income, need for medical care, self-recognition of forgetfulness, and residential area, the hazard ratios for functional disability (over long-term care level 2), dementia, and premature death increase in those with contact frequency of "less than once a month" were 1.37 (95% confidence interval [CI]: 1.16-1.61), 1.45 (95% CI: 1.21-1.74), and 1.34 (95% CI: 1.16-1.55), respectively. The "from once a month to once a week" frequency was also associated with these health indicators, although the "more than once a week" frequency was not significantly associated with any measured outcome. The prevalence of "less than once a month" contact was 7.4% (men=10.2%, women=4.7%), and this was 15.8% (men=21.2%, women=10.6%) when including those with "less than once a week" contact.
CONCLUSION: These findings suggest that "less than once a week" or "less than once a month" contact with non-cohabitant others are valid operational definitions of social isolation that are closely associated with premature death and other health indicators.